The multi-purpose beverage container holder supported tray assembly of the subject invention provides one or more utilitarian support surfaces that may be used for various functions such as eating (food and beverage placement), writing, and any of a number of other activities where a stable, conveniently positioned support surface is desired for the activity. The multi-purpose beverage container holder supported tray assembly of the subject invention is portable and is removably supported in the seat arm beverage container holders (commonly called cup holders) normally found on the seating in theaters, stadiums, indoor and outdoor sports arenas, convention halls, home entertainment centers, and the like. The multi-purpose beverage container holder supported tray assembly of the subject invention enables the user to have a secure support surface, for the placement of food and beverages, writing, or the performance of other activities, that can be easily adjusted and positioned in a location most convenient for the intended use.